Abrasive waterjet systems are used in many industries. The primary use of abrasive waterjet systems is trimming parts created by other tools. Industries often view abrasive waterjets as a rough cutting tool only. This view is too limited. The abrasive water jet is of use as a precision machining tool for such applications as drilling, turning and milling. These functions are routinely accomplished today by automated systems. Abrasive waterjets have not been widely used in automated systems for the reasons outlined below.
Waterjets are used to cut materials. A waterjet cutting system includes a source of high pressure fluid and a nozzle. The nozzle includes a pierced jewel or orifice and a housing to contain the orifice. The jet emerges from the orifice when high pressure liquid fills the housing. The jet is the actual cutting tool. Many ingenious mountings and systems of joints and seals connect the nozzle to a source of high pressure liquid. Waterjet cutting systems are routinely used to cut relatively soft materials to precise shapes. Precise cutting of sheet goods with minimal material wastage is a typical application.
Abrasive waterjets developed recently are increasingly used in manufacturing industries. An abrasive waterjet system entraps a finely divided abrasive material in a jet of high pressure liquid. First, a waterjet is created as in a waterjet cutting system. Abrasive material is supplied to the waterjet in a chamber. The waterjet with abrasive material is shaped and formed by a mixing tube before reaching the workpiece.
The nozzle for such a system must include several components. A high pressure connector is required to connect the nozzle to a supply of high pressure liquid. The high pressure connector is customarily a metal to metal seal. A jewel orifice is used for forming a waterjet. A source of abrasive and means of conveying the abrasive to the nozzle is needed. A means for mixing abrasive and the jet from the jewel orifice and forming a jet are essential functions of the nozzle. The mixing and forming functions are accomplished by an erosion resistant mixing tube. In such a nozzle the liquid pressure is very high, on the order of tens of thousands to hundreds of thousands of pounds per square inch. A suitable housing is required to hold all these components together.
As would be expected in such a system various portions wear with use. In particular, jewels, although made of extremely hard materials, break or erode. The mixing tube is exposed to rapidly moving abrasive. This causes the mixing tube to erode and require replacement. In all existing systems replacement of the jewel and/or mixing tube requires disassembly of the nozzle system.
Disassembly and subsequent reassembly is done by hand on current nozzle systems. Hand assembly is needed because the high pressures used require the use of metal to metal seals for assembly of the housing. Metal to metal seals demand a high tightening torque for assembly. This is because the pressure between the seal members must be greater than the difference between internal and external pressures. The various components of the nozzle must be very accurately aligned . Minor misalignment of the jewel, jewel mount or mixing tube can adversely affect the operation of the system. The dual requirements of high torque and accurate alignment demand hand assembly.
The necessity for periodic manual disassembly of the nozzle limits the use of abrasive waterjets in automated systems. In order to replace the worn components the system must be turned off and manufacturing interrupted. The worn part must be replaced by hand and the device reassembled. This stops the manufacturing process. In a production line this is intolerable. If automated replacement of worn components were possible abrasive waterjets could be used in many more manufacturing applications. Consequently, there is a demand for an abrasive waterjet system adapted to automated control.
In addition to automated replacement of worn components an automated system requires a means of detecting when the component must be replaced. In current manual systems the worker knows when a mixing tube or orifice must be replaced because the device stops functioning, In an automated system this is too late. Consequently, provision must be made for monitoring the condition of components prone to wear.